LAS VEGAS -- Amir Khan made it look easy.

He used his speed and his height advantage and thoroughly dominated Zab Judah. And that was before he landed a hard right hand on the beltline and knocked him out in the fifth round to unify junior welterweight titles Saturday night at the Mandalay Bay Events Center.

Ever since England's Khan stormed the American shores in May 2010, he has said he wanted to fight the best the 140-pound division had to offer.

It's not just lip service. He's doing it.

He got warm with a dominant knockout of former titlist Paulie Malignaggi in Malignaggi's hometown of New York. Then he came to the same Mandalay Bay ring in December and survived a grueling battle with Marcos Maidana in the 2010 Boxing Writers Association of America fight of the year.

After a stay-sharp defense back home in England in April, Khan returned to the United States and was determined to fight the best fighter the division had to offer.

He was supposed to face two-belt titleholder Timothy Bradley Jr., but Bradley had a change of heart and declined the fight despite a generous 50-50 offer from Khan -- including 50 percent of British television money, an almost unheard of concession. That's how much Khan wanted to fight the one 140-pounder widely ranked ahead of him.

With Bradley out of the picture, that left the resurgent Judah, a three-time 140-pound titlist and a former undisputed welterweight champion. After tough times in recent years at welterweight, Judah moved back to junior welterweight last summer and claimed a vacant belt in March by knocking out Kaizer Mabuza. When Bradley declined to fight Khan, Judah -- with Hall of Famer Pernell Whitaker in his corner -- to got the call.

But Judah looked every bit of his 33 years. He had nothing for Khan, who peppered him with hard shots to the head and body and boxed circles around him.

The first round had not even ended and already Judah's face was beginning to get marked up, in part from an accidental head butt that left him blinking his right eye.

But Khan did not let up. He really turned it up in the fifth round, snapping Judah's head back with a left hand. He continued to pound Judah during the round.

Finally, Khan nailed Judah with a right hand to the face and followed with a body shot. The right hand landed directly on the belt line in the middle of Judah's waistband and he dropped to his knees near the ropes.

Judah seemed to indicate that it was a low blow and made no serious attempt to rise as referee Vic Drakulich counted. And counted. And counted. He reached 10 at 2 minutes, 47 seconds and Judah looked surprised to be counted out as he jumped up.

It was too late.

"Zab is a great fighter, but he was a little awkward," Khan said. "I knew he was getting hurt and moving away and ducking. I kept hitting him right on the face and the shot that took him down hit him right on the belt. If it had gone another few rounds, I would have knocked him out with a clean shot. I saw I was hurting him and it was only a matter of time."

Replays showed the knockout punch was clearly a clean shot, even if Judah and Main Events promoter Kathy Duva did not agree.

"It was a low blow," Judah said. "I was trying to get myself together [when I was down] and that was self defense there [going down]. He jabbed my cup. It was an uppercut and it lifted the belt and that really hurt."

While Judah (41-7, 28 KOs), who earned $500,000, believes it was a low blow and, therefore, a controversial ending, nothing could be further from the truth because Khan (26-1, 18 KOs) dominated.

He was leading by a 40-36 shutout on all three scorecards at the time of the knockout. It looked as though Judah was in for a beating had he stayed on his feet.

Still, there was the low-blow defense.

"The punch was clearly below his belt," Duva said.

Actually, it wasn't. They can go watch the replays while Khan will move on to bigger business.

At 24, he is one of the rising stars of boxing and continues to prove it fight after fight by taking tough opponents.

"I think my speed overwhelmed him along with my power," Khan said. "I built it up from the beginning and took my time. I could've gone with the plan to knock him out sooner, but I wanted to work my way up. I'm No. 1 in the division. Now I will go back and see who my team is going to line up for me next."

He has said repeatedly he wants to fight the best and that is what he is doing. So when he says he wants to move up to welterweight, probably next year, and fight Floyd Mayweather Jr., it sure sounds legitimate.

He won't fight pound-for-pound king Manny Pacquiao because they are training partners and friends under the guidance of trainer Freddie Roach, but there are lots of options.

But it probably won't be Bradley, who ultimately rejected a 50-50 deal that would have paid him perhaps as much as $1.8 million.

"If Bradley didn't want to fight then, he probably doesn't want to fight him now after seeing what he just did to Zab Judah," Golden Boy promoter Richard Schaefer said.

Bradley, however, did not close the door on fighting Khan, despite being in the midst of a lawsuit filed by co-promoters Gary Shaw and Ken Thompson for breach of contract related to him turning down the fight with Khan. It could keep him on the sideline for some time.

"He's not ready for the 'Storm,'" Bradley said after the fight, referring to his nickname "Desert Storm."

"I'm not impressed," Bradley continued. "I know the comments that are going to be made about this, but I'm not stressing over what everyone else is saying. When we do get in the ring everyone will see who the best 140-pounder in the world is."

Whether Khan faces Bradley next or not, the plan calls for Khan -- whose official purse filed with the Nevada commission was $1,072,500, although he will make more from British television revenue -- to fight again in the United States in December. That is under the terms of his deal with HBO, Schaefer said.

"We'll see who will be available," Schaefer said. "It might be the winner of [the Aug. 27] Robert Guerrero-Marcos Maidana fight. It might be Erik Morales. But I really don't think Bradley wants to have anything to do with Amir Khan. It was a great performance. The combinations, what a talented fighter.

"One more fight at 140 and then in the spring move up to 147 and go get one of the big boys."

It sure would be nice to see Bradley first, but welterweight -- and even bigger fights -- beckon.